Abstract: I am going to explain gently how one can define link invariants using braid groups and their representations as matrices. Then I am going to explain how representations endowed with a compatible symplectic form give rise to link invariants with values in the Witt ring of the field considered; of course I will define the Witt ring as well. The construction makes use of Maslov indices. In the end, using the Burau representation, we get one invariant which "contains" many others: signatures, Jones metaplectic nvariants, and a polynomial which is almost the one by Alexander-Conway.